Revised Abstract: Pulmonary surfactant maintains the integrity of the alveoli by reducing surface tension at the alveolar air-tissue interface and plays important roles in host defense and inflammation in the lung. Surfactant protein B (SP-B), a hydrophobic protein of surfactant, is essential for the surface tension reducing function of surfactant. Inadequate production of SP-B leads to the development of newborn respiratory distress syndrome (newborn RDS) in premature infants. Reduced SP-B levels and increased nitric oxide (NO) production in the lung are associated with acute respiratory distress syndrome (ARDS) and acute pulmonary infections. NO is clinically used to treat a variety of lung disorders in adults and infants. Thus the respiratory epithelium can be exposed to elevated levels of endogenous or exogenous NO that can impair its function. Elevated levels of NO can adversely affect SP-B gene expression in the lung contributing to lung injury. The long-term objectives of this proposal are to elucidate molecular mechanisms that mediate nitric oxide inhibition of SP-B gene expression in lung H441 cells. In Specific Aim 1, a. cis-DNA elements and interacting transcription factors that mediate nitric oxide inhibition of human SP-B promoter activity will be identified, b. Molecular mechanisms underlying reduced DNA binding activities of TTF-1 and HNF-3 factors in NO treated H441 cells will be investigated. In Specific Aim 2, a. the involvement of MEK/ERK and PI3-K signaling pathways in mediating nitric oxide inhibition of SP-B gene expression will be analyzed, b. the involvement of TTF-1 and HNF-3 factors as targets for MEK/ERK and PI3-K pathways, respectively, to mediate transcriptional repression of SP-B gene expression will be investigated. The proposed studies should provide significant new information on molecular mechanisms that mediate nitric oxide inhibition of SP-B gene expression. Such information may facilitate the development of newer therapies to treat lung dysfunction due to SP-B deficiency that occurs under conditions of elevated nitric oxide production in the lung.